1. Field of the Invention
This invention relates generally to reciprocating piston type internal combustion (I.C.) engines for motor vehicles. More specifically it relates to I.C. engines having variable compression ratio connecting rods.
2. Background Information
A gasoline engine whose compression ratio remains invariant as operating conditions change is said to be knock-limited. This means that the compression ratio built into the engine design must be selected to avoid objectionable engine knock that would otherwise occur during certain conditions of engine operation if the compression ratio were larger. However, those conditions that give rise to engine knocking in a motor vehicle typically prevail for only limited times as the vehicle is being driven. At other times, the engine could operate with better efficiency, and still without knocking, if the compression ratio could be made higher, but unfortunately the engine is incapable of achieving more efficient operation during those times because its compression ratio cannot change.
Certain technologies relating to reciprocating piston I.C. engines having variable compression ratio pistons and connecting rods are disclosed in various patents, including U.S. Pat. Nos. 1,875,180; 2,376,214; 4,510,895; 4,687,348; 4,979,427; 5,562,068; and 5,755,192. Various reasons for employing such technologies in I.C. engines have been advanced in those documents. One reason is to improve efficiency by enabling an engine that is relatively more lightly loaded to run at a compression ratio that is higher than a compression ratio at which the engine operates when running relatively more heavily loaded.
The compression ratio of an engine can be varied by varying the overall effective length of a connecting rod and piston. Change in overall effective length may be accomplished in either the connecting rod, or the piston, or in both. The foregoing patents describe various mechanisms for varying overall effective length.
U.S. Pat. No. 5,562,068 discloses a variable compression ratio connecting rod where adjustment of effective length takes place at the large end. Adjustment is performed via an eccentric ring that is generally coincident with a crank pin, but can be selectively locked to the crank pin and to the large end of the rod. When locked to the crank pin, the eccentric ring assumes a position that causes the rod to have a longer effective length and hence a higher compression ratio. When locked to the rod, the eccentric ring assumes a position that causes the rod to have a shorter effective length and hence a lower compression ratio.
The present invention relates to further improvements in variable length connecting rods of reciprocating piston I.C. engines for varying engine compression ratios as engine operating conditions change. In particular the invention contemplates constructions for effecting length change at the large end of a connecting rod so that the incorporation of variable compression ratio by length change does not adversely contribute to the reciprocating mass of an engine in a way that might otherwise create unacceptable imbalance.
A general aspect of the invention relates to a variable length connecting rod assembly for imparting a variable compression ratio to an internal combustion engine. The assembly contains a first part, a second part, and a third part assembled together to form the large end of the connecting rod assembly and provide a variable length for the connecting rod assembly. The first part is a semi-circular cap. One of the second and third parts is fastened tight to the first part. Guides disposed at opposite sides of the large end operatively relate the other of the second and third parts and the fastened parts to provide for relative sliding motion between the other of the second and third parts and the fastened parts over a limited adjustment range to change the length of the connecting rod assembly.
Further aspects will be seen in various features of two presently preferred embodiments of the invention that will be described in detail.